1. Field of the Invention
This invention relates to a method for electrolyzing hydrochloric acid for the formation of chlorine, and specifically, provides a method for electrolyzing hydrochloric acid, in which the electrolyzing voltage is low, the current efficiency is high and the ratio of utilization of hydrochloric acid as a raw material is high, and which is not likely to pose a problem of pollution by the waste material discharged.
2. Description of the Prior Art
Chlorine is widely used for water treatment in sterilizing or disinfecting tap water, sewage, industrial and household effluents and water used for various types of particular purposes, and for oxidizing or bleaching treatments of various substances. Chlorine is also used in the chlorination of organic compounds. Transportation of chlorine in gas bombs is dangerous, however. In particular, when it is desired to use a large quantity of chlorine gas continuously, the danger of handling and storage of chlorine gas is the greatest problem in using chlorine gas.
For this reason, a chlorine-generating apparatus at a site adjacent a water treatment facility so that the generated chlorine can be used in situ is desirable.
Electrolysis of hydrochloric acid at a site adjacent a water treatment facility may be feasible as one particular means of achieving this. At this time, it is desirable to produce chlorine economically by minimizing the electrolyzing voltage for hydrochloric acid, maintaining the current efficiency high and utilizing the starting hydrochloric acid effectively, and to prevent pollution by the waste material discharged.
When dilute hydrochloric acid after the termination of electrolysis is to be discarded after neutralization with alkali, it is necessary for the hydrochloric acid after the termination of electrolysis to have the lowest possible concentration and to be present in a small amount from an economic standpoint. However, when hydrochloric acid is electrolyzed until the concentration of hydrochloric acid becomes very low, the electrolyzing voltage becomes high, and the current efficiency is decreased due to the generation of oxygen. Thus, the concentration of hydrochloric acid should be maintained at a point above a certain limit. Thus, it has been difficult to obtain chlorine economically using conventional methods of electrolyzing hydrochloric acid.
As a method for reducing the electrolyzing voltage positively, addition of various metal salts to the electrolytic solution has been suggested (for example, as disclosed in Japanese Patent Publications Nos. 26606/70, and 27514/74). However, this method has the disadvantage that additional expenses are involved in the treatment of waste liquors for control of pollution.
A method which involves bubbling hydrogen chloride gas into hydrochloric acid of a low concentration after the electrolysis has also been suggested. However, since hydrogen chloride gas is used as a material in this method, hydrogen chloride gas under high pressure must be transported and stored, and a problem of safety arises.